Levamisole for Cow: Uses, Dosing & Side Effects

This information is for educational purposes only. Never give your pet any medication without your veterinarian's guidance. Dosing, frequency, and safety depend on your pet's specific health profile.

Levamisole is a dewormer used in cattle to treat certain nematodes, including stomach worms, intestinal worms, and lungworms. It belongs to the imidazothiazole class of anthelmintics and works by disrupting nerve signaling in susceptible parasites, which helps the animal pass them. In the U.S., cattle products have included oral drench formulations such as Prohibit and LevaMed, and a prescription injectable combination with doramectin marketed for beef cattle and some replacement dairy heifers.

This medication has a narrower safety margin than some other cattle dewormers. That means accurate body-weight estimates, correct product selection, and careful handling matter. Your vet may choose levamisole when parasite testing, herd history, or local resistance patterns suggest it is a reasonable option, especially when rotating away from other dewormer classes.

Levamisole is not a one-size-fits-all product. Age, production class, pregnancy status, milk use, slaughter plans, and whether the product is oral or injectable all affect whether it is appropriate. Your vet can help match the product and timing to your herd’s parasite risk and residue-avoidance needs.

In cattle, levamisole is labeled for treatment of susceptible stomach worms such as Haemonchus, Trichostrongylus, and Ostertagia; intestinal worms including Cooperia, Nematodirus, Bunostomum, and Oesophagostomum; and lungworms such as Dictyocaulus. Some injectable combination products that include levamisole also cover a broader group of parasites, including certain external parasites, because of the second active ingredient.

Your vet may discuss levamisole when there is concern about dewormer resistance. Merck notes that levamisole use increased as resistance to other chemical families became a larger problem in production animals. In real-world herd medicine, that often means levamisole is considered as part of a larger parasite-control plan rather than as a stand-alone answer.

It is important to remember that deworming should be tied to a reason. Fecal egg counts, pasture history, age group, body condition, and clinical signs all help your vet decide whether treatment is likely to help. In some cattle, especially adults with low parasite burdens, monitoring and targeted treatment may make more sense than routine whole-herd dosing.

Levamisole dosing in cattle depends on the exact product and route. For FDA-approved oral drench products such as Prohibit, the labeled cattle dose is a single oral drench of 2 mL per 100 lb body weight after proper mixing, which corresponds to about 8 mg/kg levamisole hydrochloride. Label directions stress that careful weight estimates are essential, and cattle under constant parasite exposure may need re-treatment in 2 to 4 weeks if your vet recommends it.

For the prescription injectable combination doramectin + levamisole used in eligible cattle, federal labeling lists 6 mg/kg levamisole hydrochloride given subcutaneously in the neck as part of the fixed-dose product. That product is not interchangeable with oral drench dosing, and it also has important class restrictions, including limits for dairy cattle and calves.

Do not estimate casually. Because levamisole has a relatively narrow safety margin, underdosing can reduce effectiveness and encourage resistance, while overdosing raises the risk of toxicity. Your vet may recommend weighing representative animals, using a scale tape only as a rough guide, and confirming meat or milk withdrawal instructions before treatment.

Withdrawal times also matter. For Prohibit oral drench, FDA approval documents list a 2-day slaughter withdrawal in cattle. Combination injectable products have different restrictions and longer slaughter withdrawal periods, so your vet should confirm the correct label for the product actually being used.

At labeled doses, some cattle may show temporary cholinergic-type signs, especially mild hypersalivation or muzzle foaming for a few hours after treatment. Because levamisole acts on parasite nerve function and can affect the animal in similar ways when exposure is too high, side effects often look like overstimulation of the nervous system.

More concerning adverse effects can include muscle tremors, ataxia, agitation, frequent urination, frequent defecation, rapid breathing, weakness, collapse, or recumbency. Merck notes that levamisole toxicity is largely an extension of its antiparasitic effect and can cause salivation, tremors, ataxia, urination, defecation, and collapse. Injectable use generally requires extra caution because the margin for error is smaller.

See your vet immediately if your cow develops marked drooling, tremors, trouble standing, breathing changes, severe diarrhea, or collapse after treatment. Bring the product label, the amount given, the route used, and the animal’s estimated weight. That information helps your vet assess whether the problem is a medication reaction, overdose, or another illness happening at the same time.

Levamisole can interact with other products that affect cholinergic or nicotinic signaling. Product safety information for cattle combination products warns that recent treatment with cholinesterase inhibitors such as organophosphates or with morantel may enhance levamisole’s toxic effects. Older pharmacology references and toxicology literature also discuss interactions with other dewormers that have similar neuromuscular effects.

In practical terms, your vet should know about any recent or planned use of organophosphate insecticides, other dewormers, and any combination parasite-control products. This is especially important in beef operations where pour-ons, injectables, oral drenches, and feed-through products may all be used seasonally.

Do not stack dewormers on your own unless your vet has a specific reason and a dosing plan. Combination therapy can be useful in some resistance-management situations, but it needs to be intentional. The safest approach is to give your vet a full medication and pesticide history for the individual animal or herd before treatment.